ESTRO 2022 - Abstract Book

S347

Abstract book

ESTRO 2022

Results Pre-treatment factors such as alcohol intake, smoking history and P16 status were not statistically significant between asymptomatic and dysphagia groups (p>0.1775). The pharyngeal constrictor volume increased over treatment for both asymptomatic (1.60±1.54cc) and dysphagia groups (1.42±1.82cc). No changes in accumulated mean dose larger than 5% to the pharyngeal constrictors were observed (Figure 1). The maximum accumulated mean dose exhibited by the dysphagia and asymptomatic groups were 103.9% and 103.3% respectively with some inter-fraction variability amongst patients. A 10-patient subset analysis examined pharyngeal constrictor isotropic margin expansions (±1mm, ±3mm) to evaluate nearby dose gradients. A 3mm expansion margin was chosen to replicate the largest pharyngeal constrictor thickness change observed in the literature. The expansion structure D1% metrics were not significantly different from the original plan (p>0.204). No points fell outside of the 5% error with the margin expansions (Figure 2). In the patients examined, the pharyngeal constrictors are not adjacent to the high dose region.

Figure 1 . Left is the ratio of fraction-to-planned mean dose while right is the ratio of accumulated–to-planned mean dose for each patient. No patients exceeded an accumulated mean dose of 105%.

Figure 2. Expansion and original D1% dose plotted for the ±1mm and ±3mm expansions added to the pharyngeal constrictors of a 10-patient subset. There are no dosimetric changes larger than 5% and hence no large dose gradients near the original structures. Conclusion No patients in this study indicated pharyngeal constrictor mean accumulated dose changes sufficient (>5%) to suggest adaptive radiation therapy as an intervention to reduce patient reported dysphagia.

PD-0405 Analysis of the internal motion of the urethra caused by urethral catheters

D. Sevillano 1 , A. Hervás 2 , R. Rodríguez-Patrón 3 , J.D. García-Fuentes 4 , R. Colmenares 4 , C. Vallejo 2 , F. López-Campos 2 , J.A. Domínguez-Rullán 2 , T. Muñoz 2 , M. Cámara 4 , B. Capuz 4 , R. Morís 4 , P. Galiano 5 , P. Retorta 4 , S. Williamson 4 , M.J. Béjar 4 , D. Prieto 4 , F. García-Vicente 4